Many industrial processes require solid particles to be separated from a continuous liquid phase. In gravity separators, a slurry stream comprising liquid and solid particles is delivered to a vessel where the solid particles settle by gravity and are removed from the bottom of the vessel, while the clarified liquid is removed from the top of the vessel.
In the case of bitumen recovery, mined oil sand is typically mixed with warm water. The resulting slurry is piped to a primary gravity separation vessel PSV where the coarse solids fall to the bottom, a middlings stream containing some bitumen, fine solids and water is removed from the middle of the vessel and a froth containing bitumen, water and some fine mineral solids is removed from the top of the PSV. Typically, the froth comprises about 60% bitumen, 30% water and 10% fine solids.
The froth is further processed for removal of water and solids from the bitumen to permit further processing of the bitumen. It is known to use centrifuges, gravity separation vessels and inclined plate settlers to separate the bitumen from the water and the solids. The froth is typically diluted with a hydrocarbon solvent to reduce the viscosity and density of the oil phase prior to this further processing.
One such known froth separation process is taught in Canadian Patent 2,502,329 to Tipman et al. In this case, multiple stages of separation occur in three separate froth separation vessels which are utilized in a counter-current process for removal of water and solids from bitumen froth. Bitumen froth is diluted with solvent and added to the first froth separation vessel. The underflow is removed, mixed with additional solvent and is pumped to the second froth separation vessel. The overflow from the second vessel is returned to the first vessel and the underflow is mixed with additional solvent and is pumped to the third froth separation vessel. The overflow from the third vessel is pumped to the second vessel and the underflow is removed for tailings handling. The overflow from the first vessel is removed to a separation vessel for removal of solvent therefrom and the bitumen recovered is pumped to a facility for upgrading.
It is known to use both naphthenic and paraffinic solvents to reduce the viscosity and density of the oil phase of bitumen froth. In the case of paraffinic solvents, when sufficient solvent is added, asphaltenes are rejected from the froth upon contact between the solvent and the heavy hydrocarbon fraction. Large aggregates typically form between the water droplets, mineral solids and the rejected asphaltenes.
Centrifuges are typically energy intensive and gravity separation vessels generally have a very large footprint. Multiple gravity separation vessels, generally used with bitumen froth diluted in a light solvent, increase the probability and risk of breach of containment and have a large footprint. Inclined plate settlers typically have a smaller footprint however, as with the other separation equipment, more than one are required to increase the recovery of bitumen. Often combinations of the various apparatus are used in an attempt to optimize bitumen recovery.
Thus, conventional methods of separation are typically costly, require multiple pumps and other auxiliary equipment and require large volumes of solvent, for each of the separation units employed.
There is interest in froth separation apparatus and methods which are cost and energy effective, have a smaller footprint and which result in enhanced bitumen recovery therefrom.